1. Field of the Invention
The invention relates to a device for supplying secondary air into an exhaust passage, of an engine, upstream of an exhaust purification device arranged in the exhaust passage.
2. Description of the Related Art
A known engine is comprises an exhaust purification device including a catalyst having an oxidizing ability in an exhaust passage for purifying carbon monoxide (hereinafter, referred to as “CO”), hydrocarbon (hereinafter, referred to as “HC”) and nitrogen monoxide (hereinafter referred to as “NO”) contained in an exhaust gas. Further, a technique for supplying air from an air pump into a secondary air supplying passage connected to the exhaust passage and having an opening-closing valve therein to supply the air as secondary air into the exhaust passage to increase the concentration of the oxygen in the exhaust gas, thereby facilitating the oxidation of HC and CO contained in the exhaust gas and thus purification of the exhaust gas, is known.
Japanese Unexamined Patent Publication No. 2003-83048 discloses a secondary air supplying device comprising an air pump, an opening-closing valve and a check valve along the flow direction of the secondary air. In the disclosed secondary air supplying device, a pressure sensor is arranged between the air pump and the opening-closing valve or between the opening-closing valve and the check valve. In such a device, when malfunction occurs in components such as the air pump and the opening-closing valve, the efficiency for purifying the exhaust gas decreases and an exhaust emission gets worse. Therefore, in the device, it is judged if the malfunction of the components occurs on the basis of the pressure detected by the pressure sensor and/or the variation of the pressure.